JP3500868B2 - Switching regulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a switching regulator for reducing voltage. 2. Description of the Related Art Conventionally, a switching regulator for reducing voltage has been used as a device for obtaining a DC voltage lower than the voltage of a DC power supply (for example, a power supply obtained by rectifying a commercial power supply or a battery). As is well known, this switching regulator for voltage reduction supplies a DC voltage from a power supply to a switching element, turns the switching element on and off, rectifies and smoothes the output voltage of the switching element, and lowers the output voltage of the switching element to be lower than the power supply voltage. DC voltage is being obtained. FIG. 5 shows an example of a basic circuit configuration of a conventional series-type voltage-reducing switching regulator using a switching transistor as a switching element. A DC voltage Vi from a power supply (not shown) is supplied to the collector of a switching npn transistor Q via an input terminal Pin. In the prior art shown in FIG. 5, the connection point between the input terminal Pin and the collector of the transistor Q is grounded via a smoothing capacitor C2, and the base of the transistor Q is connected to the secondary of the insulating transformer T. Connected to the emitter of this transistor Q via a winding. The emitter of the transistor Q is grounded via a rectifying diode D, and the emitter of the transistor Q is grounded via a series circuit of a choke coil L and a capacitor C1 constituting a smoothing circuit. An output terminal Pout is derived from a connection point between the choke coil L and the capacitor C1. [0006] One end of a primary winding of the insulating transformer T is connected to the collector of a driving npn transistor Q2 for driving, and the other end of the primary winding of the insulating transformer T is connected to a positive direct current. Connect to power supply terminal + Vcc to which voltage is supplied. Further, the emitter of the transistor Q2 is grounded, and the drive signal input terminal 1 is led out from the base of the transistor Q2. The drive signal input terminal 1 is supplied with a square wave drive signal having a predetermined duty ratio according to a desired DC voltage Vo obtained at the output terminal Pout. In this case, when the driving signal is at the high level "1", the transistor Q2 is turned on and a current flows through the primary winding of the insulating transformer T. At this time, the switching transistor Q is turned on. When this drive signal is at the low level "0", the transistor Q2 is turned off and no current flows through the primary winding of the insulating transformer T, so that the switching transistor Q is turned off at this time. In the switching regulator shown in FIG. 5, a DC voltage Vo obtained by reducing the input DC voltage Vi according to the duty ratio of the square wave of the drive signal supplied to the drive signal input terminal 1 is applied to the output terminal Pout. I got it. In the conventional switching regulator for voltage reduction as shown in FIG. 5, a driving circuit such as a driving switching transistor Q2 and an output circuit on the emitter side of the switching transistor Q are provided. Since it is necessary to separate DC and DC from each other, an insulating transformer T is used. As the insulating transformer T, it is necessary to design an exclusive transformer for each type of switching regulator so as to be adapted to the type, which leads to complicated design work of the entire switching regulator. I was Further, the existence of the insulating transformer T is as follows.
The increase in the number of parts has led to an increase in cost and an increase in the burden of parts management. In view of the above, an object of the present invention is to provide a switching regulator which does not require such an insulating transformer. A switching regulator according to the present invention supplies a first DC voltage from a power supply to a switching element via a primary side of a bifilar-wound transformer. One end on the secondary side of the wound transformer is grounded, the other end is connected to the output terminal via a rectifier diode, and the output of this switching element is
It is supplied to this output terminal and this bifilar winding transformer
Primary and the switching element and the
With the secondary side of the wrapped transformer and this rectifier diode
Are connected via a coupling capacitor . According to this switching regulator,
Since the circuit for driving the switching element and the output circuit have the same AC potential, the drive circuit and the output circuit can be directly connected. Therefore, it is not necessary to use an insulating transformer as in the related art. Further, the bifilar-wound transformer in this switching regulator does not have to be individually designed for each type of switching regulator unlike the conventionally provided insulating transformer.
In addition, it also functions as a choke coil forming a part of the smoothing circuit (that is, the choke coil is not required instead of providing the bifilar-wound transformer). Therefore, the presence of this transformer does not complicate the design work or increase the number of parts. Embodiments of the switching regulator according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows an example of a basic circuit configuration of a switching regulator according to the present invention. A DC voltage Vi from a power supply (not shown) is supplied from the input terminal Pin to the collector of the switching npn transistor Q via the primary side of the transformer T2 wound in a bifilar configuration. The connection point between the input terminal Pin and the collector of the transistor Q is grounded via a smoothing capacitor C2. The bifilar winding transformer T2-2
On the next side, one end is grounded and the other end is a diode D for rectification.
And a ground through a series circuit of the capacitor C1 and an output terminal Pout is derived from a connection midpoint between the rectifying diode D and the capacitor C1. This bifilar winding transformer T2
The connection point between the secondary side and the collector of the switching transistor Q, and the connection point between the secondary side of the bifilar-wound transformer T2 and the rectifying diode D are connected via a coupling capacitor C4. A drive signal input terminal 1 is derived from the base of the switching transistor Q. A drive signal of a square wave having a predetermined duty ratio according to a desired DC voltage Vo obtained at the output terminal Pout is supplied to the drive signal input terminal 1 via a coupling capacitor C3 provided for cutting a DC component. . The base and the emitter are connected via a resistor R in order to make the base and the emitter of the transistor Q equipotential when the drive signal is at the low level "0" and to surely turn off the transistor Q.
Further, the emitter of the transistor Q is connected to a connection point between the rectifying diode D and the capacitor C1. In this case, when the drive signal is at the high level "1", the transistor Q is turned on and a current flows through the primary winding of the bifilar-wound transformer T2. , A voltage is generated on the secondary side of the transformer T2 based on the current flowing through the secondary winding. On the other hand, when the drive signal is at the low level "0", the transistor Q2 is turned off, and no current flows through the primary winding of the insulating transformer T, so that no voltage is generated on the secondary side of the transformer T2. Accordingly, a voltage is generated in a square wave on the secondary side of the transformer T2 by the on / off operation of the transistor Q. This square-wave voltage generated on the secondary side of the bifilar-wound transformer T2 is connected to a rectifying diode D
The current is rectified and smoothed by the series circuit of the secondary winding of the transformer T2 and the capacitor C1 which constitute the smoothing circuit. Thus, in the switching regulator shown in FIG. 1, the DC voltage obtained by reducing the input DC voltage Vi at the output terminal Pout in accordance with the duty ratio of the square wave of the drive signal supplied to the drive signal input terminal 1 Voltage V
o can be obtained. Next, the fact that the switching regulator shown in FIG. 1 is equivalent to the switching regulator shown in FIG. 5 will be described with reference to FIGS. In the switching regulator shown in FIG. 1, the switching transistor Q and the rectifier diode D are in series with the primary side and the secondary side of the transformer T2, respectively.
1 is equivalent to a circuit in which the switching transistor Q and the rectifier diode D are replaced on the opposite side of the transformer T2 as shown in FIG. Next, the circuit shown in FIG.
Is equivalent to a circuit connected as shown in FIG. The circuit in FIG. 3 is a circuit in which the transformer T2 is replaced with a choke coil L as in FIG. 4 (a circuit in which the secondary side of the transformer T2 is removed).
Is equivalent to As described above, the portion surrounded by a dashed line in FIG. 1 is equivalent to the circuit of FIG. 4, but the circuit of FIG. 4 has the same configuration as the portion of the switching regulator of FIG. is there. Therefore, the switching regulator of FIG. 1 is equivalent to the switching regulator shown in FIG. Further, according to the switching regulator of FIG. 1, since the circuit for driving the switching transistor Q and the output circuit on the emitter side of the switching transistor Q have the same AC potential, the driving circuit and the switching The output circuit on the emitter side of the transistor Q can be directly connected. Therefore, it is not necessary to use an insulating transformer as in the related art. As a result, the complexity of designing the switching regulator as a whole due to the necessity of individually designing such insulating transformers is reduced, and as is clear from the comparison between FIG. 1 and FIG. Thus, the number of parts of the switching regulator can be reduced. In this embodiment, the present invention is applied to a series type switching regulator for voltage reduction. However, the present invention is not limited to this. For example, the output voltage Vo is supplied to a feedback amplifier, and The present invention is applied to a switching regulator that stabilizes the level of an output voltage Vo by inputting a drive signal whose duty ratio is controlled based on a comparison between a predetermined reference voltage and an output voltage Vo to the base of a switching transistor. You may make it. The present invention is not limited to the above embodiment,
It goes without saying that various other configurations can be adopted without departing from the gist of the present invention. As described above, according to the switching regulator of the present invention, since the circuit for driving the switching element and the output circuit have the same AC potential, the drive circuit and the output circuit have the same potential. Can be directly connected. Therefore, it is not necessary to use an insulating transformer as in the related art. As a result, there is an advantage that the complexity of designing the switching regulator as a whole due to the need to individually design such insulating transformers can be reduced. Further, there is an advantage that the cost of the switching regulator can be reduced and the burden of parts management can be reduced by reducing the number of parts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an example of a basic configuration of a switching regulator according to the present invention. FIG. 2 is a diagram showing an equivalent circuit of a part of FIG. FIG. 3 is a diagram showing an equivalent circuit of FIG. 2; FIG. 4 is a diagram showing an equivalent circuit of FIG. 3; FIG. 5 is a circuit diagram showing an example of a basic configuration of a conventional series-type switching regulator for voltage reduction. [Explanation of Signs] Q, Q2 switching transistor, L choke coil, D rectifier diode, C1, C2 smoothing capacitor, C3, C4 coupling capacitor, R resistor, T insulating transformer, T2 transformer

Claims (1)

(57) [Claim 1] A first DC voltage from a power supply is supplied to a switching element, the switching element is turned on / off, and an output voltage from the switching element is rectified and smoothed to obtain a first DC voltage. 2. A switching regulator that obtains a DC voltage of 2. The first DC voltage is supplied to the switching element via a primary side of a bifilar-wound transformer, and one end of a secondary side of the bifilar-wound transformer is supplied to the switching element. Ground and connect the other end to output terminal via rectifier diode
Supply the output of the switching element to the output terminal
And the primary side of the bifilar winding transformer and the
A switching element and the bifilar-wound transformer
And the rectifier diode is a coupling capacitor.
A switching regulator characterized in that the switching regulator is connected via a switch.